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Image Resolution for Inkjet Printing

For people with a background in traditional graphic arts, one thing that may be hard to get used to is that the image resolution requirements for large format inkjet printer are different from those for traditional printing. The recommended resolution for lithographic printing at normal viewing distance is twice the screen ruling or 300-350 ppi for commercial quality work. However, this applies to images seen at normal viewing distance, i.e. 14 inches.

In large format, many images are obviously reproduced at larger sizes for viewing at longer distances. A commonly used formula says that the viewing distance for a document is normally equal to the diagonal. That is, if you produce a 3-4 foot poster, people could be expected to view this at a distance equal to the diagonal, which is a little more than 4 feet. Recommended resolutions range from 200 ppi at normal viewing distance to 50 ppi for a large billboard that is far away. The recommendations start at 200 ppi and not 300-350 because resolution requirements are lower for inkjet, since it uses stochastic screening (halftone process based on random distribution dots).

A good example of this is a movie poster that is intended to be viewed from several feet away. Up close, the poster may look pixelized, but when standing back, you cannot see the pixels.